Gasifiers with non radial tuyeres

ABSTRACT

A gasifier for the manufacture of producer gas has a chamber ( 10 ) for the combustion of material, the chamber ( 10 ) being provided with a plurality of tuyeres ( 30 ) for the introduction of combustion air to the chamber. The tuyeres ( 30 ) are disposed at an acute angle to the wall of the chamber ( 10 ) so that air is directed both around and upwardly of the chamber. Each tuyeres ( 30 ) is configured to produce a jet stream wherein the air swirls along the length of the stream.

CROSS REFERENCE TO RELATED APPLICATION

The present application is the U.S. National Stage Application ofInternational Application PCT/GB99/01671, filed May 27, 1999, whichinternational application was published on Dec. 2, 1999 as InternationalPublication WO99/61561 in the English language. The InternationalApplication claims priority of Great Britain Application 9811415.0,filed May 28, 1998.

BACKGROUND OF THE INVENTION

This invention relates to gasifiers and in particular to improvements inor relating to gasifiers whereby improved combustion may take placetherewithin. The invention further relates to a method of operating agasifier.

The production of producer gas (a mixture of about 30% carbon monoxideand 70% nitrogen, though other gases may also be present) is usuallyperformed with a so-called gasifier, in which pyrolysis is performed.The gasifier comprises a chamber provided with air inlets in such a waythat the burning of fuel within the chamber take place under controlledconditions. Originally, gasifiers used coal or coke as a fuel source,but interest in gasifiers has recently increased since they may be usedfor the disposal of various kinds of waste organic solid matter whilstyielding producer gas, which in turn may drive a combined heat and powerunit, to yield both heat and electricity. Thus, the solid fuel maytypically comprise wood or wood derivatives, straw, poultry litter,dried sewage sludge and refuse-derived combustible material, to mentionbut a few.

In a gasifier chamber, the solid fuel is reduced to a bed of carbon at atemperature of above 1000° C., a stream of air being passed through thebed with the combustion conditions set so that the oxygen in the aircombines with the carbon to form carbon monoxide. Other gases such asmethane and hydrogen may also be produced, depending upon the chemicalcomposition of the fuel employed.

A product of the combustion in a gasifier is ash, but this is ofrelatively low density and of small volume compared to the solid fuelsupplied to the gasifier. It is consequently relatively easy to disposeof, especially since it is wholly sterile. By contrast, the producer gasmay be used for a variety of purposes, though since it is toxic in viewof the carbon monoxide content, it must nevertheless be treated withcare. For example, the collected producer gas may immediately be used inan internal combustion engine for the generation of electricity, withoutbeing stored for long periods or otherwise handled.

Though the principle upon which a gasifier operates is well known andunderstood, it is important that the combustion conditions are closelycontrolled in order that the production of carbon monoxide is optimisedand that the carbon dioxide content of the producer gas is minimised. Ithas now been established that by controlling the actual introduction ofair into the oxidation zone of a gasifier, it is possible to improve thegasifier performance, so increasing the overall efficiency of plantusing this equipment.

Gasifier designs have been proposed in NL-A8900939 and CH-A-237348. Inboth of these prior designs, arrangements are made to introducecombustion air into a gasifier in such a way that the air is notdirected strictly radially with respect to the axis of the combustionchamber, in an attempt to enhance combustion within the chamber. Thepresent invention stems from attempts further to improve the productionof producer gas.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided agasifier for the production of producer gas from combustible material,comprising a chamber into which said material is introduced and aplurality of tuyères disposed at or adjacent the lower end of thechamber for the introduction of air into the combustion chamber, eachsuch tuyère defining an axis along which air is projected into thechamber, at least some of the tuyères being configured to impart arotational motion about said axis along which the air is projected intothe chamber from each such tuyère, whereby the combustion air isprojected in the form of a jet stream which swirls about the length ofthe stream.

Preferably, at least some of the tuyères are disposed with theirrespective axes at an acute angle (when projected on to a horizontalplane containing the respective tuyère) to a tangent to the wall of thechamber at the location of that tuyère, the axis of projection of eachsaid tuyère being in the same sense with respect to the axis of thechamber, whereby the projected air also tends to swirl around thechamber.

It will be appreciated that the gasifier of this invention is able toachieve better reduction of the fuel, by improving the interactionbetween the introduced air and the hot carbonised bed at the bottom ofthe gasifier chamber. This interaction may be achieved either solely bycausing the introduced air to rotate along the axis of projection intothe gasifier, or by additionally causing the introduced air to swirlaround the lower region of the chamber. By adopting both of thesemeasures of this invention, the interaction of the air with the bed atthe bottom of the gasifier is much enhanced, so giving better control ofthe combustion of the fuel. In turn, this leads to more completecombustion in the oxidation zone, giving a greater oxygen deficiency inthe reduction zone and raising the proportion of carbon monoxide in theresultant producer gas.

Most preferably, all of the tuyères lie at substantially the same acuteangle to the chamber wall where the respective tuyère projectstherethrough. Thus, by having the angle of projection of each saidtuyère in the same sense with respect to the axis of the chamber, theintroduced air tends to swirl around the chamber interacting with allportions of the relatively hot carbon bed. This effect is enhanced byproviding the tuyères in a uniform distribution equi-spaced around thechamber.

Advantageously, each tuyère is directed both at a non radial angle tothe axis of the chamber and also upwardly of the chamber. In this way,penetration of the entire hot carbon bed by the introduced air may beassured.

The chamber may be of general circular cross-sectional shape, at leastin the region of the tuyères, with the axis of the chamber extendinggenerally vertically. That chamber may have a lower wall of a generallyconical shape and which supports a bed of the combustible material, saidtuyères being mounted in that lower conical wall. At the other end ofthe chamber, there may be provided an inlet orifice for combustiblematerial, the upper portion of the chamber serving as a hopper for thematerial loaded thereinto. The inlet orifice advantageously is fittedwith a slide valve, to permit charging of the hopper whilst the gasifieris in operation.

Each tuyère is preferably in the form of a nozzle projecting through thechamber wall, the bore of the nozzle being configured to cause the airflow therethrough to rotate about its length. This may be achieved byproviding an insert within each said nozzle, the insert comprising aplate the width of which is substantially the same as the nozzleinternal diameter and the plate being twisted along its length.

This invention extends to a method of operating a gasifier for theproduction of producer gas from combustible material, which gasifiercomprises a chamber into which said material is introduced and aplurality of tuyères disposed at or adjacent the lower end of thechamber, in which method air is introduced into the combustion chamberthrough the tuyères and each tuyère is configured to impart a rotationalmotion about the axis of introduction of the air so that the combustionair is projected in the form of a jet stream which swirls about thelength of the introduced stream. In addition, the invention provides forthe air being introduced through tuyères at least some of which havetheir respective axes at an acute angle (when projected onto ahorizontal plane containing the respective tuyère) to a tangent to awall of the chamber at the location of that tuyère, whereby the air willtend to swirl around the chamber, simultaneously with the rotation ofthe air about its own axis.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

By way of example only, one specific embodiment of gasifier constructedand arranged in accordance with the present invention will now bedescribed in detail, reference being made to the accompanying drawingsin which:

FIG. 1 is a diagrammatic vertical section through the embodiment of thegasifier;

FIG. 2 is a plan view on the lower wall of the gasifier chamber shown inFIG. 1, with parts removed for clarity;

FIG. 3 is a detailed view on an enlarged scale through said lower wall;

FIG. 4 is an end-view on a tuyère of the gasifier of FIGS. 1 to 3; and

FIG. 5 illustrates an insert plate of the tuyère nozzle of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1, there is shown diagrammatically anembodiment of gasifier arranged for the production of producer gas froma solid combustible material serving as a fuel, such as wood chippings,logs, coal or similar materials, poultry litter, dried sewage sludge ora refuse derived fuel. The gasifier comprises a combustion chamber 10having a generally conical lower wall 11 provided with a flange 12around its upper periphery. A hopper 13 has a corresponding flange 14 atits lower periphery and which is secured by bolts (not shown) to flange12 of the lower wall 11. The upper end of the hopper 13 is closed by aslide valve assembly 15, which permits recharging of the hopper withmore solid fuel whilst operation of the gasifier continues. An actuator15A is mounted to one side of the hopper, to effect opening and dosingof the slide valve assembly.

In an alternative arrangement (not shown) the hopper has a simple lidwhich may be secured in position and a fuel feed arrangement may beprovided to supply fuel into the upper part of the hopper.

The lower wall 11 is carried on a base structure 16 which defines aplenum chamber 17 provided with an air inlet 18 and six lighting ports19, each normally closed by a respective cap 20, the ports 19 beingequi-spaced around the plenum chamber 17. The central region of thelower wall 11 communicates through opening 22 with a tube 23 withinwhich the producer gas is formed during operation of the gasifier, thetube 23 leading to a lower chamber 24. A producer gas outlet pipe 25passes through an outer wall 26 of the lower chamber 24 and there isprovided a port 27 to that chamber, normally closed by a blanking plate28 but through which access to the chamber may be gained for example forash removal and servicing.

An automated ash removal system is fitted below the tube 23. Thiscomprises an eccentric grate assembly 40 mounted on a shaft 41 rotatablysupported below the base wall of the lower chamber 24. The shaft 41 alsocarries a scraper bar 42 having chains which serve to plough collectedash into a discharge chute 43 below lower chamber 24. A motor 44 isdrivingly connected by chain 45 to the shaft 41 to effect rotation ofboth the grate assembly 40 and the scraper bar 42. A discharge auger 46takes discharged ash from the chute 43, through a water seal provided atthe bottom of that chute.

Air enters the plenum 17 through inlet 18 and passes into the combustionchamber 10 through a plurality of tuyères 30, provided in the conicallower wall 11 of the chamber. As best seen in FIG. 2, six such tuyères30 are provided, equi-spaced around the opening 22 in alignment with thelighting ports 19. The tuyères all lie at substantially the same angleto the vertical axis 31 of the combustion chamber 10 and also all lie atsubstantially the same angle to a horizontal radius of the chamberintersecting the respective tuyère. Thus, air entering the combustionchamber will tend to swirl around the chamber in a counter-clockwisedirection and at the same time to rise upwardly within the chamber.

Each tuyère 30 is fitted with an insert 33 so as to impart a spin on thejet of air issuing from the tuyère into the combustion chamber 10. Theinsert is in the form of a plate having a width substantially equal tothe diameter of the tuyère, as shown in FIG. 4, and is twisted through90° along its length. In this way, the air passing through the tuyèrewill be caused to swirl about the axis of the tuyère.

In operation, solid fuel pieces are loaded into the hopper 13 throughthe slide valve assembly 15 and then the air flow is commenced byreducing the pressure at the producer gas outlet 25. This draws airthrough inlet 18 into the plenum 17, the air then swirling around thatplenum 17 and assisting cooling of the lower plate 11, when operation ofthe gasifier has been established. From the plenum 17, the air is drawnthrough the tuyères 30 into the bed on the lower wall 11 and downthrough opening 22, tube 23 and into the lower chamber 24 by the reducedpressure at the producer gas outlet 25. The gasifier is lit through atleast one of the ports 19, for example with a gas torch, and thecombustion within the chamber 10 is established. When fully operational,the upper region 35 of the gasifier will be at around 500° C. and willserve as a distillation zone for high molecular weight hydrocarbons.Below that, there is a carbonisation zone 36 operating at around 600°C., where the solid fuel is converted to charcoal, by burning off othermatter. On and immediately above the lower wall 11, there is establishedan oxidation zone 37, operating at around 1200° C., where the carbon isburned in air to form CO₂. The hot carbon then falls through opening 22into tube 23 and on to grate 40, there being a deficiency of oxygen inthe tube 23 to continue the combustion of the carbon and so a reductionprocess takes place, reducing the CO₂ to CO. The final producer gasmixture leaves the lower chamber 24 through pipe 25.

During operation of the gasifier, the motor 47 is operatedintermittently slowly to drive the grate assembly 40. The eccentricityof this assembly grinds any large pieces which then fall through thelower chamber 24 and are ploughed into the discharge chute 43. The motormay be operated continuously, depending upon the ash content of the fuelsource.

A typical producer gas composition obtained from using wood as a fuelsource may be as follows:

GAS % by weight Nitrogen 45-54 carbon monoxide 18-25 hydrogen 13-15water vapour 10-15 carbon dioxide  5-10 methane 3-5

By adopting the measures as described above concerning the dispositionof the tuyères and also the internal configuration thereof, and soimproving the introduction of air into the oxidation zone through thetuyères, it is found the carbon dioxide content may significantly bereduced, with a consequent improvement in the carbon monoxide content ofthe producer gas.

1. A gasifier for the production of producer gas from combustiblematerial, comprising a chamber into which said material is introducedand a plurality of tuyères disposed at or adjacent the lower end of thechamber for the introduction of air into the combustion chamber, eachsuch tuyère defining an axis along which air is projected into thechamber, at least some of the tuyères being configured to impart arotational motion about said axis along which the air is projected intothe chamber from each such tuyère, whereby the combustion air isprojected in the form of a jet stream which swirls about the length ofthe stream.
 2. A gasifier as claimed in claim 1, wherein at least someof the tuyères are disposed with their respective axes at an acute angle(when projected on to a horizontal plane containing the respectivetuyère) to a tangent to the wall of the chamber at the location of thattuyère, the axis of projection of each said tuyère being in the samesense with respect to the axis of the chamber, whereby the projected airalso tends to swirl around the chamber.
 3. A gasifier as claimed inclaim 2, wherein said at least some of the tuyères lie at substantiallythe same acute angle to the respective tangents to the chamber wall atthe location of the respective tuyères.
 4. A gasifier as claimed inclaim 2, wherein said axis of projection of each tuyère is directedupwardly of the chamber in addition to being directed with its axis atan acute angle to a tangent of the wall when projected on a horizontalplane containing that tuyère.
 5. A gasifier as claimed in claim 1,wherein all of said tuyères are similarly configured and disposed withrespect to the chamber.
 6. A gasifier as claimed in claim 1, wherein thechamber is generally of circular cross-sectional shape at least in theregion of the tuyères with the axis of the chamber extending generallyvertically.
 7. A gasifier as claimed in claim 6, wherein the gasifierchamber has a lower wall of generally conical shape which supports a bedof the combustible material, said tuyères being mounted in the lowerwall.
 8. A gasifier as claimed in claim 1, wherein said tuyères aredistributed substantially uniformly around the chamber.
 9. A gasifier asclaimed in claim 1, wherein each said tuyères includes a nozzle whichprojects through the chamber wall, the bore of the nozzle beingconfigured to cause the air flow therethrough to rotate about said axisof the tuyère.
 10. A gasifier as claimed in claim 9, wherein an insertis provided within each said nozzle, the insert comprising a plate thewidth of which is substantially the same as the nozzle diameter and theplate being twisted along is length.
 11. A method of operating agasifier for the production of producer gas from combustible material,which gasifier comprises a chamber into which said material isintroduced and a plurality of tuyères disposed at or adjacent the lowerend of the chamber, in which method air is introduced into thecombustion chamber through the tuyères and each tuyère is configured toimpart a rotational motion about the axis of introduction of the air sothat the combustion air is projected in the form of a jet stream whichswirls about the length of the introduced stream.
 12. A method asclaimed in claim 11, wherein the tuyères are disposed with theirrespective axes at substantially the same acute angle (when projectedonto a horizontal plane containing the respective tuyère) and in thesame sense to a tangent to a wall of the chamber at the location of thattuyère whereby air introduced to the chamber through the tuyères tendsto swirl around the chamber.
 13. A method as claimed in claim 11,wherein the air is drawn through the tuyères by reducing the pressure atthe producer gas outlet of the gasifier.
 14. A method as claimed inclaim 12, wherein the air is drawn through the tuyeres by reducing thepressure at the producer gas outlet of the gasifier.
 15. A gasifier asclaimed in claim 3, wherein said axis of projection of each tuyere isdirected upwardly of the chamber in addition to being directed with itsaxis at an acute angle to a tangent of the wall when projected on ahorizontal place containing that tuyere.
 16. A gasifier as claimed inclaim 7, wherein said tuyeres are distributed substantially uniformlyaround said chamber and each said tuyere includes a nozzle whichprojects through the chamber wall, the bore of the nozzle beingconfigured to cause the air flow therethrough to rotate about said axisof the tuyere.